This invention relates to the field of musical instruments and tuners therefor, and more particularly to a tuner having the capability of shifting an entire scale instantly by predetermined scale increments.
Programmable musical instruments such as those described in U.S. Pat. No. 3,821,460 and No. 3,939,751 have been programmed by manually resetting the appropriate switches in a bank of 120 switches per keyboard (manual or pedal). In U.S. Pat. No. 4,085,645, instant scale changing capability was added to such instruments by the use of DC programmable counters with DC switching. In another U.S. Pat. No. 3,876,936, a visual frequency comparator includes a CRT display device having a "split-screen". All of the patents listed above are assigned to the same assignee as is the present invention. Two audio frequencies can be compared on the screen by causing each signal to produce a horizontal bar pattern on a respective half of the screen. One set of bars is "synced" to provide a motionless reference pattern. If the other set of bars is also motionless the two frequencies being compared are either identical or have a relationship which is the ratio of two whole numbers; e.g., 3:2, 2:1. The respective numbers of bars denotes the frequency ratio, i.e., if three bars on the "unknown" side of the screen occupy the same space as two bars on the reference side, the ratio is 3:2 (the unknown frequency ratio is a perfect fifth above the reference). Relative motion indicates by direction the "sharp" or "flat" quality of the unknown frequency relative to the reference. The reference tone is normally internally generated but, if desired, another instrument can supply the reference.
A difficulty encountered with the above-described frequency comparator tuning device derives from the fact that different musicians and musical organizations vary in their choice of frequency for a given scale note. Most scales are based on the choice of frequency for the note designated "A" above middle "C".
The so-called "concert pitch" for this note is 440 Hz, but in actual use the pitch of the "A" may vary several hertz, depending generally on the conductor. It is therefore desirable to be able to tune "A" to any number (usually an integer) of hertz (cycles per second) within a range of 435 Hz to 446 Hz, and without manual reprogramming.
It is also desirable to shift the entire scale simultaneously without affecting the set intervals. The semitone interval in Equal Temperament, as in most music in the western world today, comprises a ratio of tones 1:1.06. For example, the frequency of "A#", the next note above "A", would be 1.06 times the frequency of A, regardless of the actual frequencies involved, 1.06 being the twelfth root of two and 2:1 being the ratio of an octave interval.